A light control member formed by a prism sheet 5 is arranged along an emitting surface 12 of a light guide plate of a side light type surface light source device for liquid-crystal display backlighting arrangement and the like. The prism sheet 5 is provided with numerous projections formed with a height H1 at a pitch D1. Roughness is imparted to the emitting surface 12 by matt-processing or adhesion of fine particles. The roughness is preferably within the arithmetic average roughness Ra range 0.02-0.25 μm. Non-uniformity may be applied to height H1 of the prism sheet 5. The tendency of the prism sheet to adhere to the emitting surface is reduced and degradation of light quality prevented by the roughness of the emitting surface and/or non-uniform height of projections on the prism sheet.
|
1. A side light type surface light source device comprising:
a light guide plate having an edge surface and an emitting surface to emit light having directivity; a light source that supplies light to the light guide plate via the edge surface; and a sheet-shaped light control member which is arranged along the emitting surface of the light guide plate, the light control member having a prismatic face to correct the directivity; wherein the prismatic face of the light control member faces the emitting surface and is provided with numerous prismatic projections formed of repeating slopes inclined with to respect the emitting surface, the prismatic projections having non-uniform heights, so that a first portion of the prismatic projections is separated from the emitting surface and a second portion of the prismatic projections is in direct contact with the emitting surface.
2. A surface light source device of side light type according to
3. A side light type surface light source device according to
4. A side light type surface light source device according to
|
This application is a divisional application of application number 08/801,805, filed Feb. 14, 1997, now pending
1. Field of Invention
The present invention relates to a side light type light source device for use with a liquid-crystal display or the like, and more particularly to a side light type surface light source device that employs a light guide plate having emitting directivity.
2. Related Art
Side light type surface light source devices have a thin structure and have previously been applied to backlighting of liquid-crystal display panels and the like.
A side light type surface light source device is equipped with a light guide plate, and a rod-shaped light source (primary light source) such as a cold-cathode tube arranged along an edge of the light guide plate. Light emitted by the primary light source is introduced through an edge of the light guide plate into the light guide plate. The light introduced into the light guide plate is deflected and output from one face of the light guide plate to illuminate, for example, a liquid-crystal panel.
Light guide plates employed in side. light type surface light source devices are classified basically into two types by shape. One of these types of light guide plate has a substantially uniform thickness, while the other type of light guide plate has a thickness that has a tendency to decrease gradually from one edge. It is known that the. latter type can emit light generally more efficiently than the former type.
The reflection sheet 4 is a sheet-shaped regular reflection member formed of gold foil or the like, or a sheet-shaped irregular reflection member formed of white PET film or the like.
The light scattering guide plate 2 has a wedge-shaped cross-section. The material of the light scattering guide plate 2 is obtained by uniformly distributing light-permeable fine particles, for example, in a polymethylmethacrylate (PMMA) matrix having a different refractive index from that of the light-permeable fine particles.
The light L is thus subjected to this scattering and nears the tip of the light scattering guide plate 2 as it is reflected between the surface on the reflection sheet 4 side (hereinafter referred to as the "sloping surface") and the surface on the prism sheet 5 side (hereinafter referred to as the "emitting surface").
In this propagation process the angle of incidence of the light L relative to the emitting surface is reduced little by little each time the light L is reflected by the sloping surface. Components satisfying the condition of being at or below the critical angle relative to the emitting surface exit from the emitting surface. Based on the above-described scattering, light L1 exiting from the emitting surface, as shown in
As shown in
Prism sheet 5 is arranged to correct this directivity. Prism sheet 5 is formed of light-permeable sheet material such as polycarbonate, with the prism surface facing the light scattering guide plate 2 (i.e. inwardly). The prism surface is comprised of numerous triangular-cross-section projections extending substantially parallel to the incident surface T of the light scattering guide plate 2. The sloping surfaces of these triangular projections correct the principal emission direction of the light L1 (i.e. preferential propagation direction) to the front of the emission surface.
The prism sheet 5 may be a double-sided prism sheet. A double-sided prism sheet is one that has another prism surface on the side opposite to the light scattering guide plate 2 side (outside surface). The grooves on the outside prism surface are substantially at right-angles to the grooves on the inside prism surface. A surface light source device 1 that employs these prism sheets emits light to the front with good efficiency, compared with side light type surface light source devices that employ a light guide plate of substantially uniform thickness.
Light guide plates having emitting directivity include wedge-shaped or nearly wedge-shaped light guide plates comprised of a transparent or semi-transparent material, and flat-plate-shaped light guide plates having a scattering film or the like on the emitting surface, or on the reverse surface, or on both surfaces. A side. light type surface light source device that employs a plate such as these also is able to emit light to the front with good efficiency.
The present inventors observed that if this type of side light type surface light source device is placed in a high-temperature environment for a long time, various patterns appear on the prism sheet 5 (that is, on the illuminant surface of the side light type surface light source device), as shown in FIG. 8. This phenomenon can be explained as follows.
When a prism sheet 5 is exposed to a high-temperature environment for a long time, the prism sheet 5 tends to exhibit local adhesion to the emitting surface of the light scattering guide plate 2. In regions where the prism sheet 5 adheres to the emitting surface, the layer of air between the prism sheet 5 and the emitting surface is lost. This results in disturbances in the thickness distribution of the air layer, thereby providing the pattern appearance.
Island-shaped patterns C as shown in
The aim of the present invention is to resolve the above problems of the prior art. The object of the present invention is to provide a side light type surface light source device that can prevent adhesion of a light control member such as a prism sheet to the emitting surface, thereby avoiding reduction in illumination light quality.
In accordance with this invention, means to prevent adhesion between the emitting surface of the light guide plate used in the side light type surface light source device is applied to at least one of the light guide plate and a plate shaped control member emitting surface and the light control member.
The adhesion prevention means applied to the emitting surface is embodied as an emitting surface having a roughness that does not disorder the emitted light. The emitting surface roughness may be provided by roughening the emitting surface itself or by adhering numerous fine particles to the emitting surface.
The adhesion prevention means applied to the light control member is embodied as providing the light control member with projections having various heights, thereby effectively avoiding the light control member from adhesion.
The roughness imparted to the emitting surface preferably within arithmetic average roughness Ra range from 0.02 to 0.25 μm. Such a roughness may be applied by roughening the emitting surface itself or by adhering numerous fine particles to the emitting surface.
In accordance with this invention, the roughness of the emitting surface holds diffusion of emitted light to within a range that is small enough for practical purposes, maintaining the directivity of the emitted light. Providing such a roughness on the emitting surface effectively prevents adhesion by lowering the affinity between the light control member and the emitting surface.
A light control member with projections of various heights causes the space between each projection and the emitting surface to vary accordingly. The result is that affinity between Light control member and emitting surface is lowered, effectively preventing adhesion. This technique does not reduce emitted light directivity.
The invention will now be described in further detail with reference to the accompanying drawings.
With reference to
The roughness imparted to emitting surface 12 effectively prevents the prism sheet 5 disposed closely along the emitting surface 12 from adhering to the emitting surface 12.
In accordance with this structure, contact between emitting surface 12 and prism sheet 5 is via the projecting portions of the surface roughness. As a result, affinity (tendency to adhere) between prism sheet 5 and emitting surface 12 is greatly reduced compared with an emitting surface 12 having no roughness.
It should be noted that the roughened emitting surface 12 may possibly scatter the emitted light and reduce its directivity.
Curve M1 shows the characteristics obtained when the emitting surface is a mirror surface; curve M2 is for an emitting surface with an arithmetic average roughness Ra of 0.2 μm, and curve M3 is for an emitting surface has an arithmetic average roughness Ra of 0.3 μm. It is seen from these curves that curve M2 hardly shows decrease in emitting directivity compared with M1 while curve M3 shows a remarkable decrease in emitting directivity. The peak (frontal luminance) of curve M3 is approximately 10% lower than the peak (frontal luminance) of curve M1.
In order to compare peaks with respect to other roughnesses, luminance was measured perpendicular to the emitting surface with arithmetic average roughness Ra as a parameter and the graph of
The graph shows that an arithmetic average roughness Ra of 0.25 μm or more out of a range indicated by AR in FIG. 4,; and provides rapid reduction in directivity and frontal luminance level. Such a striking decrease in directivity is undesirable for practical use.
The inventors left a surface light source device 1 incorporating a prism sheet 5 and light scattering guide plates provided with different roughnesses for 1000 hours in an environment with a temperature of 70°C C. and a humidity of 20%, and then checked them for adhesion of the prism sheet 5. It was found that the divide between adhesion and non-adhesion was at an arithmetic average roughness Ra of 0.02 μm and adhesion arises in the case of an emitting surface having a roughness closer to a mirror surface (low roughness) than that value while no adhesion arises under such roughness as greater than that value.
Based on the above, an actual preferred condition for the emitting surface to effectively prevent adhesion of the prism sheet 5 without degradation of directivity is within an arithmetic average roughness Ra range of from 0.02 to 0.25 μm.
With reference to
The height variation of the projections on the prism sheet 15 may be based on a non-regular height distribution or on a regular height distribution in which various heights are included.
The roughness of the emitting surface 12 of the light scattering guide plate 11 in the first embodiment described above may be applied by a means other than matt-processing. For example, sand-blasting or chemical etching may be used to effect the roughening.
The light scattering guide plate 11 with roughness does not always require the emitting surface 12 itself. The emitting surface 12 may, for example, be roughened by adhering many fine particles to the emitting surface 12 to be roughened. Adhesion of the fine particles may be effected by, for example, printing ink containing fine particles on the emitting surface. The fine particles are preferably transparent, and preferably not larger than 30 μm in diameter. The emitting surface 12 produced by the adhesion of fine particles, as in the case in which matt-processing is used, preferably has an arithmetic average roughness Ra in the range from 0.02 to 0.25 μm.
The first and second embodiments can be used in combination to impart roughness to the emitting surface 12 and non-uniform heights to the prism sheet projections. It will probably be readily understood from the preceding explanation that such an arrangement will further enhance the effective prevention of prism sheet adhesion.
Prisms may be provided on both sides of the prism sheets 5 and 15 used as the light control member.
While it is preferable to use a light scattering guide plate with a wedge-shaped cross-section, a flat plate can also be applied to the invention.
In the arrangements of the first and second embodiments, light is supplied to the light scattering guide plate from one end, but this may be modified. For example, light may be supplied by arranging a light source such as light source 3 (see
It should be noted that the application of the surface light source device of this invention is not limited to liquid-crystal display backlighting arrangements but may also be applied to the lighting arrangements of various other lighting devices, display devices and the like.
Ishikawa, Tsuyoshi, Noguchi, Nobuhisa
Patent | Priority | Assignee | Title |
10310162, | Dec 01 2015 | Samsung Display Co., Ltd. | Optical component and display device having the same |
11755123, | Feb 04 2021 | Lite-On Technology Corporation | Illuminated keyboard |
7384173, | Dec 30 2004 | 3M Innovative Properties Company | Brightness enhancement article |
7404659, | Nov 21 2006 | Chien-Chin, Mai; Gamma Optical Co., Ltd. | Backlight module |
7744263, | Dec 16 2004 | Microsharp Corporation Limited | Structured optical film |
7800301, | Sep 06 2004 | UDC Ireland Limited | Organic electroluminescent device comprising a prism structure |
8553175, | Apr 14 2006 | Saturn Licensing LLC | Optical sheet having irregularity portions, backlight device with optical sheet, and liquid crystal display device including a backlight device with optical sheet |
8670088, | Apr 14 2006 | Saturn Licensing LLC | Optical sheet comprising a base composed of a stack of transmissive sheets, and a back-light device and liquid crystal device incorporating the optical sheet |
Patent | Priority | Assignee | Title |
4617245, | Feb 09 1984 | Canon Kabushiki Kaisha | Light receiving member having tapered reflective surfaces between substrate and light receiving layer |
4737896, | Jul 23 1985 | Canon Kabushiki Kaisha | Illumination device |
4948690, | Jun 19 1986 | Canon Kabushiki Kaisha | Electrophotographic photosensitive member with fine spherical resin powder |
5123077, | Mar 20 1989 | Hitachi, Ltd. | Light source device |
5384658, | Sep 04 1990 | Ohno Research & Development Laboratories Co. Ltd. | Plastic optical member and light-quantity-controlling member each having a light-diffusing layer on its surface |
5704703, | Mar 03 1993 | Sharp Kabushiki Kaisha | Lighting device and display device using the lighting device |
5851062, | Aug 11 1995 | Omron Corporation | Prism sheet for surface light source |
5919551, | Apr 12 1996 | Minnesota Mining and Manufacturing Company | Variable pitch structured optical film |
5944405, | Aug 12 1994 | Dai Nippon Printing Co., Ltd. | Flat light source using light-diffusing sheet with projections thereon |
6104454, | Nov 22 1995 | PANASONIC LIQUID CRYSTAL DISPLAY CO , LTD | Liquid crystal display |
6396634, | Feb 20 1996 | Enplas Corporation; KOIKE, YASUHIRO | Surface light source device of side light type |
EP544332, |
Executed on | Assignor | Assignee | Conveyance | Frame | Reel | Doc |
Oct 17 2000 | Enplas Corporation | (assignment on the face of the patent) | / | |||
Oct 17 2000 | Yasuhiro Koike | (assignment on the face of the patent) | / |
Date | Maintenance Fee Events |
May 12 2006 | M1551: Payment of Maintenance Fee, 4th Year, Large Entity. |
May 03 2010 | M1552: Payment of Maintenance Fee, 8th Year, Large Entity. |
Jan 27 2014 | RMPN: Payer Number De-assigned. |
Jan 30 2014 | ASPN: Payor Number Assigned. |
May 12 2014 | M1553: Payment of Maintenance Fee, 12th Year, Large Entity. |
Date | Maintenance Schedule |
Nov 12 2005 | 4 years fee payment window open |
May 12 2006 | 6 months grace period start (w surcharge) |
Nov 12 2006 | patent expiry (for year 4) |
Nov 12 2008 | 2 years to revive unintentionally abandoned end. (for year 4) |
Nov 12 2009 | 8 years fee payment window open |
May 12 2010 | 6 months grace period start (w surcharge) |
Nov 12 2010 | patent expiry (for year 8) |
Nov 12 2012 | 2 years to revive unintentionally abandoned end. (for year 8) |
Nov 12 2013 | 12 years fee payment window open |
May 12 2014 | 6 months grace period start (w surcharge) |
Nov 12 2014 | patent expiry (for year 12) |
Nov 12 2016 | 2 years to revive unintentionally abandoned end. (for year 12) |